Process for flocculation of a tailings stream

ABSTRACT

A process for the treatment of a tailings stream is provided. The tailings stream comprises water, sand and clay fines and is produced from bitumen extraction process of an oil sands ore. The process for treating the tailings stream comprises contacting a polysilicate microgel, a polyacrylamide and one or both of a multivalent metal compound and a low molecular weight cationic organic polymer with a tailings stream to flocculate sand and clay fines.

FIELD OF THE INVENTION

The present invention relates to a process for extraction of bitumenfrom oil sands and flocculation/dewatering of tailings after extraction.

BACKGROUND OF THE INVENTION

Oil sands have become an attractive source of oil recovery to supportglobal demand for oil. Oil sands are large deposits of naturallyoccurring mixtures of bitumen, water, sand, clays, and other inorganicmaterials found on the earth's surface. Bitumen is a highly viscous formof crude oil. The largest oil sands deposits are found in Canada andVenezuela. In particular, the Athabasca oil sands deposit is equivalentto 1.6 to 2.7 trillion barrels of oil, and is located in the Canadianprovinces of Alberta and Saskatchewan. About 10% of the Athabasca oilsands deposit can be mined. Once the oil sands are mined, it isprocessed by extracting the bitumen.

The bitumen must be extracted and separated from the water, sand andfine clays of the oil sands. Today, the oil sands are mined, crushed,then mixed with hot water, and optionally chemicals, to facilitateextracting the bitumen from the sand and clay fines. The extractedbitumen is separated from the sands and fine clays and is then refined.The remaining sand, fine clays and water, commonly referred to as“tailings”, are further processed to dewater the sand and fine clays.The sand and clay fines are typically disposed, e.g., in a tailings pondand settle to become mature fine tailings. Mature fine tailings are astable slurry comprising clay, fine sands, water and bitumen. Maturefine tailings have no strength, no vegetative potential and can be toxicto animal life, so must be confined and prevented from contaminatingwater supplies. The recovered water from the dewatering step may bere-used in the extraction process. Faster recovery of the water reducesheat energy requirements when this water is recycled for use in theextraction process.

The recovered bitumen from this process is in the form of a froth. Thefroth comprises a concentrated bitumen (typically 50% or greater),water, fine sand and clays. The froth is treated in a froth treatmentunit, which may use steam (to de-aerate the froth) and a naphthenic orparaffinic solvent to recover a bitumen with greater than 95% purity. Abyproduct of the froth treatment process is a froth treatment tailings.The froth treatment tailings comprise water, residual solvent, and finesolids that are primarily smaller than 44 micrometers in size. The frothtreatment tailings are typically disposed of in a tailings pond. Frothtreatment tailings contribute to mature fine tailings formation.

Tipman et al., in U.S. Pat. No. 5,876,592, disclose recovery of bitumenfrom oil sands in a process comprising adding aqueous caustic to an oilsands slurry, to create an emulsion. The emulsion is allowed to separateinto 3 layers, with a top layer of a first froth comprising bitumen,bottom layer, referred to as tailings, comprising water, sand and clayfines that settled, and a middle layer, referred to as middlings,comprising residual bitumen, suspended clay fines and water. Themiddlings are further processed to recover additional bitumen in thesame manner as the oil sands slurry, producing a second froth. Thesecond froth may be combined with the first froth to recover bitumen bydilution with a solvent and removal of sand and clay fines.

Yuan, et al., Canadian Metallurgical Quarterly, 2007, vol. 46, no. 3 pp.265-272, disclose using a multiple-step process, in a particularsequence, for removing sands and fine clays from tailings. The firststep is referred to as flocculation-coagulation-flocculation (FCF), inwhich a flocculant is added. This allows for the flocculation of largerparticles leaving fines in solution. In the second step, a coagulant isadded. The coagulant destabilizes the fines causing small flocs to form.In the third step, a small amount of flocculant is added to combine thelarger flocs from the first step with the smaller flocs in the secondstep, resulting in even larger flocs and an increase of settling rates,allowing for faster dewatering.

Acidified silicate has been used to enhance bitumen extraction byMasliyah, et al., Ind. Eng. Chem. Res., 2005, vol. 44, pp. 4753-4761. Byacidifying the silicates, divalent metal ions can be sequesteredallowing for improved bitumen liberation while maintaining consistentpH. There is a similar disadvantage with this process as found in WO2005/028592, that is, solids are dispersed.

Li, et al., Energy & Fuels, 2005, vol. 19, pp. 936-943 disclose theeffect of a hydrolyzed polyacrylamide (HPAM) on bitumen extraction andtailings treatment of oil sands ores. Careful control of HPAM dosage isnecessary to achieve efficiency in both bitumen extraction and inflocculation of solid fines.

Separation of bitumen from sand and clay fines, as well as dewatering ofthe sand and clay fines for disposal, are especially difficult forso-called “poor quality ores.” Generally, a poor quality ore, inreference to an oil sands ore is an oil sands ore that contains a largeamount of fines that hinder, not only extraction of bitumen, but alsothe dewatering process of sand and clay fines. Poor quality ores aredifficult to extract bitumen from at acceptable yields usingconventional methods. In addition, more bitumen is retained in thetailings streams from extraction of poor quality ores, which is sent tothe tailings pond as a yield loss.

Poor quality ores reduce yield by as much as 35 to 50% and are avoidedwhen possible. Alternatively, poor quality ores are blended in limitedquantities with good quality ores so they can be processed moreeffectively. With demand for oil increasing every year, there is a needto mine these poor quality ores and to produce high yield of bitumen.The tailings should be essentially free of bitumen and separated fromwater, so the water can be re-used and the solids can be returned to theenvironment free of bitumen, within environmental limits.

There is a desire to have lower extraction temperatures (for example,less than about 50° C.) to save heat energy. For example, when anadjacent upgrading facility to treat the extracted bitumen is notavailable, there is added cost to supply heat energy for the extractionwater.

While there have been many advances in the oil sands extraction andtailings, there remains a need to improve bitumen recovery (yield) fromoil sands, improve de-watering of the tailings (i.e., less water in thetailings) and reduce need to add fresh water bitumen recovery processes.There is also a need to improve bitumen extraction in poor quality ores,and to do so without significant capital equipment, without significantbitumen yield loss. The present invention meets these needs.

SUMMARY OF THE INVENTION

The present invention is a process for the extraction/recovery ofbitumen from oil sands and for the treatment of tailings. In oneembodiment of this invention, the process comprises (a) providing anaqueous slurry of an oil sands ore and (b) contacting the slurry with apolysilicate microgel to produce a froth comprising bitumen and atailings stream comprising sand and clay fines. Preferably, the processfurther comprises (c) dewatering the tailings. Bitumen is recovered fromthe froth. Optionally, an anionic polyacrylamide and/or caustic, such assodium hydroxide, sodium silicate, sodium citrate, may be added afterstep (b) and prior to step (c). Alternatively, a polyacrylamide and oneor both of (i) a multivalent metal compound and (ii) a low molecularweight cationic organic polymer may be added after step (b) and beforestep (c). Surprisingly, the process improves recovery of bitumen anddoes not adversely affect flocculation of tailings as compared to use ofsodium silicate instead of polysilicate microgel. The polysilicatemicrogel is carried through to a dewatering step and may enhanceflocculation in said tailings.

In an alternative embodiment of this invention, there is a process fortreating a tailings stream comprising water, sand and clay fines toflocculate the sand and clay fines wherein the process comprises (a)contacting a polysilicate microgel, an anionic polyacrylamide and one orboth of (i) a multivalent metal compound and (ii) a low molecular weightcationic organic polymer with the tailings stream to produce aflocculated solid, and (b) separating the flocculated solid from thestream. Unexpectedly and advantageously, in this second embodiment,flocculation is enhanced compared to use of polyacrylamide alone.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a process flow diagram of a bitumen extraction process andtailings flocculation in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

In a first embodiment of this invention, there is provided a process forthe recovery of bitumen from oil sands which comprises providing anaqueous slurry of an oil sands ore and contacting the slurry with apolysilicate microgel to improve bitumen separation, producing a frothand a tailings. A slurry of an oil sands ore may be produced by miningan oil sands ore, crushing the ore and adding water to produce a slurry.Optionally, an anionic polyacrylamide and/or caustic, such as sodiumhydroxide, sodium silicate and sodium citrate, may be added to thecombination of oil sands ore and microgel. The froth comprises bitumen,clay fines and water. The tailings comprise sand, clay fines, unreactedpolysilicate microgel and water. Preferably the process furthercomprises dewatering the tailings. The polysilicate microgel in thetailings may be carried through with the water to a dewatering step,wherein the microgel may enhance flocculation in the tailings.

In an alternative embodiment, there is provided a process for theflocculation of a tailings stream wherein the tailings stream isproduced from an oil sands ore and comprises water, sand and clay fines.This process comprises contacting the tailings stream with apolysilicate microgel, an anionic polyacrylamide and one or both of amultivalent metal compound and low molecular weight cationic organicpolymer to flocculate the solids.

Oil Sands Ore

Oil sands ores are large deposits of naturally-occurring mixturescomprising bitumen, sand, clays, and other inorganic materials. Herein,bitumen refers to hydrocarbons and other oils found in oil sands, tarsands, crude oil and other petroleum sources. The oil sands ores used inthis invention are mined materials and typically comprise about 5 to 15wt % bitumen. The oil sands ores further comprise water, sand and clayfines. Generally the oil sands ores comprise about 2 to 5 wt % water.Inorganic material can be naturally-occurring ores, such as titaniumores and zirconium ores that are present in the oil sands ore.

The process of this invention may be used advantageously to treat poorquality ores. The “poorer” the quality of the oil sands ore, the higherthe level of clay fines. Surprisingly, the process of this invention iseffective at extracting bitumen from poor quality oil sands ores, whileeffectively dewatering the tailings streams.

Poor quality ores are defined herein as an oil sands ore which has oneor more of the following properties: (a) levels of clay fines of greaterthan 15%; (b) montmorillonite clay in an amount greater than 1 wt % ofthe total weight of the oil sands ore, (c) greater than 10 ppm ofcalcium, magnesium; and (d) ores less than 25 meters from the earth'ssurface that have been subject to oxidation.

Polysilicate Microgel

The process of this invention comprises contacting a polysilicatemicrogel with an oil sands ore. Polysilicate microgels are aqueoussolutions which are formed by the partial gelation of an alkali metalsilicate or a polysilicate, such as sodium polysilicate. The microgels,which can be referred to as “active” silica, in contrast to commercialcolloidal silica, comprise solutions of from 1 to 2 nm diameter linkedsilica particles which typically have a surface area of at least about750 m²/g. Polysilicate microgels are commercially available from E. I.du Pont de Nemours and Company, Wilmington, Del.

Polysilicate microgels have SiO₂:Na₂O mole ratios of 4:1 to about 25:1,and are discussed on pages 174-176 and 225-234 of “The Chemistry ofSilica” by Ralph K. Iler, published by John Wiley and Sons, N.Y., 1979.General methods for preparing polysilicate microgels are described inU.S. Pat. No. 4,954,220, the teachings of which are incorporated hereinby reference.

Polysilicate microgels include microgels that have been modified by theincorporation of alumina into their structure. Such alumina-modifiedpolysilicate microgels are referred as polyaluminosilicate microgels andare readily produced by a modification of the basic method forpolysilicate microgels. General methods for preparingpolyaluminosilicate microgels are described in U.S. Pat. No. 4,927,498,the teachings of which are incorporated herein by reference.

Polysilicic acid is a form of a polysilicate microgel and generallyrefers to those silicic acids that have been formed and partiallypolymerized in the pH range 1-4 and comprise silica particles generallysmaller than 4 nm diameter, which thereafter polymerize into chains andthree-dimensional networks. Polysilicic acid can be prepared, forexample, in accordance with the methods disclosed in U.S. Pat. No.5,127,994, incorporated herein by reference.

In addition to the above-described silica microgels, the term“polysilicate microgels” as used herein, includes silica sols having alow S value, such as an S value of less than 50%. “Low S-value silicasols” are described in European patents EP 491879 and EP 502089. EP491879 describes a silica sol having an S value in the range of 8 to 45%wherein the silica particles have a specific surface area of 750 to 1000m²/g, which have been surface modified with 2 to 25% alumina. EP 502089describes a silica sol having a molar ratio of SiO₂ to M₂O, wherein M isan alkali metal ion and/or an ammonium ion of 6:1 to 12:1 and containingsilica particles having a specific surface area of 700 to 1200 m²/g.

Polyacrylamide

Polyacrylamides (PAMs) useful in the present invention include anionic,cationic, non-ionic and amphoteric polyacrylamides. Polyacrylamides arepolymers formed by polymerization of acrylamide, CH₂═CHC(O)NH₂.Polyacrylamides of the present invention typically have a molecularweight greater than one million.

Preferably the PAM is an anionic polyacrylamide (APAM) or cationicpolyacrylamide (CPAM), more preferably APAM. APAM and CPAM are thegeneric names for a group of very high molecular weight macromoleculesproduced by the free-radical polymerization of acrylamide and ananionically or a cationically charged co-monomer. APAM and CPAM can beprepared by techniques known to those skilled in the art, including butnot limited to the Mannich reaction. Both the charge density (ionicity)and the molecular weight can be varied in APAM and CPAM. By varying theacrylamide/ionic monomer ratio, a charge density from 0 (nonionic) to100% along the polymer chain can be obtained. The molecular weight isdetermined by the type and concentration of the reaction initiator andthe reaction parameters.

Low Molecular Weight Cationic Organic Polymers

Low molecular weight cationic organic polymers which can be used in thisinvention have a number average molecular weight less than 1,000,000.Preferably, the molecular weight is in the range between about 2,000 toabout 500,000, more preferably between 10,000 and 500,000. The lowmolecular weight polymer is typically selected from the group consistingof polyethylene imine, polyamine, polycyandiamide formaldehyde polymer,diallyl dimethyl ammonium chloride polymer, diallylaminoalkyl(meth)acrylate polymer, dialkylaminoalkyl (meth)acrylamide polymer, acopolymer of acrylamide and diallyl dimethyl ammonium chloride, acopolymer of acrylamide and diallylaminoalkyl (meth)acrylate, acopolymer of acrylamide and dialkyldiaminoalkyl (meth)acrylamide, and acopolymer of dimethylamine and epichlorohydrin. Such polymers aredescribed, for example, in U.S. Pat. Nos. 4,795,531 and 5,126,014. Lowmolecular weight cationic organic polymers are commercially available,for example, from SNF Floerger, Andrézieux, France as FLOQUAT FL 2250and FLOQUAT FL 2449 and from FCT-Water Treatment, Greeley, Colo. asWT-530.

Multivalent Metal Compounds

Multivalent metal compounds useful in the present inventive process arecompounds of metals with more than one valence state. Examples ofmultivalent metals include calcium, magnesium, aluminum, iron, titanium,zirconium and combinations thereof. Preferably, the multivalent metalcompound is soluble in water and is used as an aqueous solution.Examples of suitable multivalent metal compounds include calciumchloride, calcium sulfate, calcium hydroxide, aluminum sulfate,magnesium sulfate, and aluminum chloride, polyaluminum chloride,polyaluminum sulfate, and aluminum chlorohydrate. Preferably themultivalent metal compound is calcium sulfate, aluminum sulfate,polyaluminum sulfate, polyaluminum chloride, or aluminum chlorohydrate.Compounds of multivalent metals that are polymerized are especiallyuseful in the present invention.

Extraction and Flocculation

Oil sands ores are generally mined from the earth and processed toremove the bitumen, which can then be further treated as a crude oil. Ina first embodiment, an oil sands ore is provided. The oil sands ore ismined from an oil sand deposit and crushed to provide a materialsuitable for extracting bitumen from the ore. Conventional methods canbe used for mining and crushing. The oil sands ore is generallyprocessed as an aqueous slurry. Recycled water from downstreamdewatering step vida infra may be used to prepare the oil sands oreaqueous slurry.

The process of this invention comprises providing an aqueous slurry ofan oil sands ore and contacting the slurry with a polysilicate microgelto extract bitumen from the oil sands ore. Water and optionally air maybe added to the slurry prior to or during this contacting (extraction)step at a temperature in the range of 25 to 90° C. (77 to 194° F.),preferably at a temperature of 35 to 85° C. (95 to 185° F.).Advantageously the contacting step is performed at a temperature of 50°C. or less, for example, 35-50° C. (95-122° F.).

The amounts of the slurry components can vary. An aqueous slurry of anoil sands ore can be prepared by contacting an oil sands ore with waterin an amount of 10% to 500%, based on the mass of the ore, preferably,50% to 200%. The water may be recycled water from the extractionprocess. The amount of water added may be determined by extractionefficiency and by limitations of transfer lines used to convey theore-containing slurry effectively through an extraction unit operation.

The polysilicate microgel is typically added in an amount of 25 to 5000g per metric ton of the oil sands ore.

One or more of the following additives may be added to the oil sands oreslurry prior to contacting with the polysilicate microgel (extractionstep (b)): anionic polyacrylamide and other polymeric flocculants andcoagulants; caustics such as sodium hydroxide, sodium silicate, andsodium citrate; organic acids and salts of organic acids, such asglycolic acid and sodium glycolate, surfactants, buffers such asbicarbonates, and antimicrobial agents.

In the extraction step (b), the oil sands ore, microgel and water aremixed and optionally contacted with air, generally in the form of airbubbles, in a reaction vessel or in a transport line. Contact of the airbubbles with the slurry results in bitumen floating to the top of theslurry, creating a top layer, referred to as a froth, or a first froth,if multiple froths are produced in the process. The (first) frothcomprises bitumen that has floated to the top of the slurry, and alsocomprises clay fines.

After forming a froth, the remainder of the slurry is permitted toseparate in the reaction vessel or is transferred from a transport lineto a separating vessel. The majority of the sand and clay fines settleto the bottom of the slurry forming a bottom layer, referred to as acoarse tailings. A middle layer is also formed in the slurry. The middlelayer is a diluted portion of the slurry comprising bitumen that did notfloat to the top and sand and clay fines that did not settle to thebottom, and is referred to as middlings.

The middlings may be removed from the middle of the reaction orseparation vessel. The removed middlings may be further processed bycontacting with air as air bubbles or passing through one or more airflotation cells, where air bubbles enhance separation of the bitumendroplets from the solids (sand and clay fines) and water of themiddlings, producing a (second) froth. The second froth may be recoverede.g., from the air flotation cell(s), and may be combined with a firstfroth. Polysilicate microgel may be added at this process step,typically in an amount of 25 to 5000 g per metric ton of the oil sandsore. Alternatively, the second froth may be added to the slurrycomprising the oil sands ore and water prior to treating the slurry toproduce the first froth.

After forming the second froth, the remainder of the slurry is permittedto separate in the reaction vessel or is transferred to a separatingvessel. The majority of the sand and clay fines settle to the bottom ofthe slurry forming a bottom layer, referred to as a fine tailings, whichcomprise less sand and more fines than coarse tailings. A middle layermay also form in the slurry. Both the middle and bottom layers may becombined and treated downstream in a dewatering step as fine tailings.

Optionally, the middle layer that is formed with the second froth isremoved as a second middlings and further treated with air in the samemanner as the (first) middlings, that is, treated with air to produce athird froth. The third froth may be combined with the first froth andsecond froth to recover bitumen. The third froth may added to the slurrycomprising the oil sands ore and water prior to producing first froth,optionally being combined with the second froth. In still anotheralternative, the third froth may be combined with the middlings prior tocontacting the middlings with air. A second fine tailings is alsoproduced with the third froth.

Each successive formation of a froth removes more of the bitumen fromthe oil sands ore. Although producing only up to a third froth isdescribed herein, successive froths (fourth, fifth, etc.) arecontemplated within the scope of this invention.

The process may further comprise removing the froth from the top of theslurry in the extraction step(s) and transferring the froth to a frothtreatment unit. In the froth treatment unit, the froth is contacted witha solvent to extract the bitumen from the froth and to concentrate thebitumen. Typically the solvent is selected from the group consisting ofparaffinic C₅ to C₈ n-alkanes and naphthenic solvents. Naphthenicsolvents are typically coker naphtha and hydrotreated naphtha having anend boiling point less than 125° C. A by-product from froth treatmentunit is froth treatment tailings, which comprise very fine solids,hydrocarbons and water.

After treatment of the froth in the froth treatment unit, theconcentrated bitumen product may be further processed to purify thebitumen.

The froth treatment tailings may be further treated in a dewatering stepto remove water, which may be recycled in the process, from the solidswhich comprise clay fines and sand.

The process may further comprise dewatering tailings. The tailings canbe one or more of any of the tailings streams produced in a process toextract bitumen from an oil sands ore. The tailings is one or more ofthe coarse tailings, fine tailings and froth treatment tailings. Thetailings may be combined into a single tailings stream for dewatering oreach tailings stream may be dewatered individually. Depending on thecomposition of the tailings stream, the additives may change,concentrations of additives may change, and the sequence of adding theadditives may change. Such changes may be determined from experiencewith different tailings streams compositions.

The tailings stream comprises at least one of the coarse tailings, finetailings and froth treatment tailings. This dewatering step comprisescontacting the tailings stream with polyacrylamide and one or both of(i) a multivalent metal compound and (ii) a low molecular weightcationic organic polymer. The tailings stream may comprise polysilicatemicrogel from the extraction steps. Additional polysilicate microgel maybe added as necessary. Polysilicate microgels enhance the flocculationof the sand and clay fines in the dewatering step by providing a betterseparation of solids from water and/or an increased rate of separationof the solids from water and/or permitting a range of operatingconditions for the dewatering step which can be tolerated while stillachieving a desired level of separation of solids from water within adesired period of time.

Dewatering may be accomplished by means known to those skilled in theart. Such means include use of thickeners, hydrocyclones and/orcentrifuges, or by decantation and/or filtration. The dewatered solidsshould be handled in compliance with governmental regulations. Theseparated water may be recycled to the process (“recycled water”). Forexample, the recycled water may be added to crushed oil sands ore forbitumen extraction. Recycled water may also be added to the process atany point where water is added.

Conventionally fine tailings and froth treatment tailings have beendifficult to dewater effectively. Both comprise clay fines andunextracted bitumen. Such tailings after dewatering, have been sent totailings pond and after time become mature fine tailings. In the presentinvention, separation of solids from even the fine tailings and frothtreatment tailings is improved.

In alternatives to the process of this invention, there is a process toextract bitumen from a slurry comprising bitumen wherein the processcomprises providing a slurry comprising bitumen, wherein the slurry is amiddlings, a fine tailings or a froth treatment tailings, contacting theslurry with a polysilicate microgel to extract bitumen from the slurry,and produce a froth comprising bitumen and tailings. Preferably thetailings are dewatered. The contacting, extracting and dewatering stepsare performed as described hereinabove.

The processes of this invention can be used to treat poor quality ores.Alternatively, a higher percentage of poor quality ores may be blendedwith good quality ores in the extraction and dewatering processes ofthis invention.

In a second embodiment of this invention, there is provided a processfor treating a tailings stream comprising sand, clay fines and water,which process comprises (a) contacting the tailings stream with apolysilicate microgel, an anionic polyacrylamide, and one or both of amultivalent metal compound and a low molecular weight cationic organicpolymer to produce flocculated solids; and (b) separating theflocculated solids from the stream. The separating step may be bydewatering. In this process, the sand and clay fines are flocculated toproduce flocculated solids. In the separating step, the flocculatedsolids are separated from the stream, e.g., by dewatering to provide thesolids and a recovered water.

The tailings stream may be a coarse tailings, fine tailings, frothtreatment tailings or a combination of two or more thereof. Processes toproduce such tailings streams are described hereinabove, with theexception that, in this embodiment, no polysilicate microgel is added inthe extraction process. Therefore, tailings streams applicable to thisembodiment can be produced from conventional oil sands processes forbitumen extraction. For example, the tailings stream treated herein canbe a slurry comprising clay fines recovered from an oil sands solventrecovery unit. Still further, as an alternative, the tailings stream maybe a mature fine tailings that has been removed from a tailings pond.

In the separating step, the objective is to flocculate and dewater thesolids, while enabling recovery of as much water as possible.Surprisingly in the present invention, a faster separation rate and morecomplete separation of the solids from the water has been achieved. Thusthe present invention has an improved process efficiency relative toconventional processes for treating tailings streams.

Solids may be disposed of, sent to a tailings pond for additionalsettling or, when solids are a concentrated source of minerals, such astitanium and zirconium minerals, the solids may be used as a rawmaterial or feed to produce for example, titanium and zirconiumcompounds for commercial products.

Order of addition of polysilicate microgel, anionic polyacrylamide andone or both of a multivalent metal compound and a low molecular weightcationic organic polymer may be varied to induce certain desiredeffects. For example, the multivalent metal compound and/or lowmolecular weight cationic organic polymer may be added first and thenthe polyacrylamide may be added to the tailings stream, that is, firstadd metal compound, then add polymer. In an alternative method, thefollowing addition sequence is used: (1) a first polymer, which is apolyacrylamide, then (2) a multivalent metal compound and/or lowmolecular weight cationic organic polymer, then (3) a second polymer,which is a polyacrylamide, are added in that sequence to the tailingsstream. The first and second polymer may be the same or differentpolymers. For example, both the first and second polymers may bepolyacrylamide; however the first polymer is an anionic polyacrylamideand the second may be a cationic polyacrylamide. In either of theaddition methods disclosed, polysilicate microgel may be added at anypoint. That is, the microgel may be added prior to or after addition ofanionic polyacrylamide and multivalent metal compound and/or lowmolecular weight cationic organic polymer, that is, prior to or afteradditions of (1), (2) and (3).

Dewatering may be accomplished by means known to those skilled in theart to separate the solids from the process water. Such means includethickener, hydrocyclone, centrifuge, decanting, and filtration. Thedewatered solids should be handled in compliance with governmentalregulations.

It has been surprisingly found that polysilicate microgels enhance theflocculation of the sand and clay fines in the dewatering step oftailings produced in the extraction of bitumen from oil sand oresrelative to known processes which use polyacrylamide alone andpolyacrylamide in combination with metal salts. Specifically, in theprocesses of this invention, solids separate from water at faster ratesthan known processes. In addition, a higher percentage of water isrecovered from the processes and the recovered water can be recycled tothe process.

It is desirable to recycle water to oil sands ore extraction andrecovery processes in order to minimize the need to use fresh water asmake-up in the processes. The recycled water may be added to crushed oilsand ore to produce a slurry for bitumen extraction. Alternatively, ifrecovered water is in excess of what is needed for the process, thewater may be returned to the environment if the water meets localstandards.

Still further, relative to known processes which use sodium silicate,the addition of polysilicate microgel during the extraction steps, doesnot adversely affect the separating/dewatering step, that is, it hasbeen reported that the presence of sodium silicate retards flocculationand separation of solids from the tailings streams. Surprisingly in thisinvention, the addition of polysilicate microgel does not have a similareffect as sodium silicate. Use of sodium silicate also reduces watervolume that is recovered and slows the rate of separation of solids fromwater relative to use of polysilicate microgels.

The processes of the present invention are robust and can be used toachieve desired levels of bitumen extraction and water recovery fromboth good and poor quality ores. Furthermore, the present inventionprovides a simpler separation process overall, reducing equipment, forexample, eliminating the need for mechanical separation equipment. Stillfurther the processes of the present invention may be used to treat finetailings, to recover bitumen from such tailings, and to provide amineral source, reducing the need for settling ponds.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 is a process flow diagram of a bitumen extraction process andprocess for tailings flocculation in accordance with this invention.

Polysilicate microgel (PSM) and crushed oil sands ore (Ore) are combinedin pipeline 1 and transferred as feed 2 to mixing vessel 3. Water isadded to mixing vessel 3, producing a slurry. Air is added to slurry inmixing vessel 3 to produce (1) first froth 4, which comprises bitumenand separates from the slurry to the top of mixing vessel 3; (2) coarsetailings 5, which comprises the majority of sand and clay fines fromfeed 2, and separates to the bottom of mixing vessel 3; and (3)middlings 6, which comprises bitumen, clay fines and sand, and is themiddle layer in mixing vessel 3.

First froth 4 is transferred to froth treatment vessel 7. Solvent isadded to treatment vessel 7 to extract bitumen 8 from first froth andalso produce froth treatment tailings 9 in treatment vessel 7. Bitumen 8is transferred from treatment vessel 7 for further processing. Frothtreatment tailings 9 comprises water and clay fines, and is furthertreated with other tailings streams.

Middlings 6 are removed from the middle of mixing vessel 3 andtransferred to second mixing vessel 3 a. Water is added to second mixingvessel 3 a. Air is added to second mixing vessel 3 a to produce secondfroth 4 a, which comprises bitumen, clay fines and water and separatesfrom middlings 6 to the top of mixing vessel 3 a, and fine tailings 10,which comprises sand, clay fines and water and separates to the lowerpart of mixing vessel 3 a. Second froth 4 a is combined with first froth4 and transferred to froth treatment vessel 7.

Coarse tailings 5 comprising sand, clay fines and water are combinedwith froth treatment tailings 9 and fine tailings 10 to provide combinedtailings stream 11 and transferred to separator 12.

Optionally, a metal compound and/or a low molecular weight cationicorganic polymer (MC/P), polyacrylamide (PAM) and polysilicate microgel(PSM) are added to combined tailings stream in separator 12. Combinedtailings stream 11 is allowed to settle in separator 12. Solids 13comprising sand and clay fines are separated from water 14. Solids 13are transferred to tailings pond. Water 14 may be recycled, such as bytransferring to mixing vessel 3 for re-use.

EXAMPLES

All solutions were stirred at 250 rpm. All filtrations were performed byfiltering through #41 filter paper available from Whatman Group, FlorhamPark, N.J. and a Bühner funnel under vacuum. All percentages are listedby weight, unless otherwise noted. The volume of liquid passing throughthe filter paper was recorded at 0.5, 1, 2, 3, 4, and 5 minutes. Thecalculated solids concentrations were calculated based on startingweight of solids divided by the starting weight of the sample, plusweight of chemical additions, less the weight of liquid passing throughthe filter.

Example 1

A clay fines slurry (2.5 g, 6.7% solids) retained from oil sands solventrecovery unit was added to a beaker. A 100 ppm (mg calcium per kgsolution) as calcium sulfate solution (87.7 mL, 2.42 g CaSO₄ in 2.5 Lwater) was prepared and added to the beaker. Water (87.7 g) was alsoadded to bring the clay solids concentration to 2% and the slurry wasstirred. An aqueous 0.1% solution of SUPERFLOC 135 (3.75 mL, 0.1%, ananionic polyacrylamide commercially available from Cytec Industries,West Paterson, N.J.) was added to the slurry and the slurry was stirred.After 30 seconds, aqueous polysilicate microgel solution (2.5 mL, 1%SiO₂, commercially available from E. I. du Pont de Nemours and Company,Wilmington, Del.) was added to the slurry and the slurry was thenstirred. After an additional 30 seconds, the stirring was stopped, andthe beaker contents were filtered. The volume of the liquid passingthrough the filter paper was recorded and a solids concentration wascalculated as described above. Calculated solids concentration resultsare in Table 1.

Comparative Example A

A clay fines slurry (2.5 g, 6.7% solids) retained from oil sands solventrecovery unit was added to a beaker. A 100 ppm (mg calcium per kgsolution) calcium sulfate solution (87.7 mL) was prepared and added tothe slurry in the beaker. Water (87.7 g) was also added to the beaker tobring the clay solids concentration in the slurry to 2% and the slurrywas stirred. An aqueous 0.1% solution of SUPERFLOC 135 (3.75 mL, 0.1%)was added to the slurry and the slurry was stirred. After an additional30 seconds, the stirring was stopped, and the beaker contents werefiltered. The volume of the liquid passing through the filter paper wasrecorded and a solids concentration was calculated as described above.Calculated solids concentration results are in Table 1.

Comparative Example B

A clay fines slurry (2.5 g, 6.7% solids) retained from oil sands solventrecovery unit was added to a beaker. Water was added to the beaker tobring the clay solids concentration in the slurry to 2% and the slurrywas stirred. An aqueous 0.1% solution of SUPERFLOC 135 (3.75 mL, 0.1%)was added to the slurry and the slurry was stirred. After an additional30 seconds, the stirring was stopped, and the beaker contents werefiltered. The volume of the liquid passing through the filter paper wasrecorded and a solids concentration was calculated as described above.Calculated solids concentration results are in Table 1.

TABLE 1 Calculated Solids Concentration (% by weight) vs. Time (minutes)0.5 min 1 min 2 min 3 min 4 min 5 min Example 1 3.99 5.80 11.05 13.7920.62 25.97 Comp. Ex. A 2.09 2.12 2.20 2.25 2.32 2.36 Comp. Ex. B 2.913.50 4.47 5.63 6.97 8.81

As can be seen in Table 1, the calculated solids concentration afterdewatering the product of Example 1 which contained 100 ppm calcium, 15ppm anionic polyacrylamide (APAM), and 100 ppm SiO₂ as polysilicatemicrogel was greater than the calculated solids after dewatering theproduct of Comparative Example A which contained 15 ppm APAM. Thecalculated solids concentration from Example 1 was also greater than thecalculated solids after dewatering the product of Comparative Example B,which contained 100 ppm calcium as calcium sulfate and 15 ppm APAM.Greater calculated solids concentration indicates an improvement indewatering efficiency.

Example 2

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. Aqueous polysilicate microgelsolution (2.5 mL, 1% SiO₂) was added to the slurry in the beaker and theslurry was stirred. A 35% aluminum hydroxide sulfate solution (0.524 mL,7.16% Al₂O₃, commercially available under the brand name PASS 100, fromCleartech Industries, Inc., Saskatoon, SK, Canada) was added to theslurry and the slurry was stirred. Sodium hydroxide (6.1 mL, 0.3 N) wasthen added to the slurry to raise the pH to 8.4. An aqueous 0.1%solution of SUPERFLOC 135 (3.75 mL) was added to the slurry and theslurry was stirred. After 15 seconds, the stirring was stopped, and thebeaker contents were filtered. The volume of the liquid passing throughthe filter paper was recorded and a solids concentration was calculatedas described above. Calculated solids concentration results are in Table2.

Comparative Example C

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. A 35% aluminum hydroxide sulfatesolution (0.524 mL, 7.16% Al₂O₃) was added to the slurry and the slurrywas stirred. Sodium hydroxide (4.4 mL, 0.3 N) was then added to theslurry to raise the pH to 8.4. An aqueous 0.1% solution of SUPERFLOC 135(3.75 mL) was added to the slurry and the slurry was stirred. After 15seconds, the stirring was stopped, and the beaker contents werefiltered. The volume of the liquid passing through the filter paper wasrecorded and a solids concentration was calculated as described above.Calculated solids concentration results are in Table 2.

TABLE 2 Calculated Solids Concentration (% by weight) vs. Time (minutes)0.5 min 1 min 2 min 3 min 4 min 5 min Example 2 3.03 4.56 13.94 20.9523.96 25.16 Comp. Ex. C 2.68 3.32 4.69 7.08 9.87 23.07

As can be seen in Table 2, the calculated solids concentration afterdewatering of the product of Example 2, which contained 100 ppm SiO₂ aspolysilicate microgel, 150 ppm Al₂O₃ as aluminum hydroxide sulfate, and15 ppm anionic polyacrylamide (APAM), was greater than the calculatedsolids after dewatering the product of Comparative Example C which didnot contain polysilicate microgel. Significantly, the rate of dewateringfor the product of Example 2 was much faster than the rate of dewateringfor the product in Comparative Example C.

Example 3

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. Aqueous polysilicate microgelsolution (2.5 mL, 1% SiO₂) was added to the slurry and the slurry wasstirred. Sodium hydroxide (0.3 mL, 0.3 N) was then added to the slurryto raise the pH to 8.4. An aqueous 0.1% SUPERFLOC 135 solution (1.25 mL)was added to the slurry and the slurry was stirred. A 35% aluminumhydroxide sulfate solution (0.035 mL, 7.16% Al₂O₃) was added to theslurry and the slurry was stirred. After 30 seconds, an aqueous 0.1%PERCOL 7651 solution (0.5 mL, a cationic polyacrylamide commerciallyavailable from Ciba Specialty Chemical Corp., Tarrytown, N.Y.) was addedto the slurry and the slurry was stirred. After 15 seconds, the stirringwas stopped, and the beaker contents were filtered. The volume of theliquid passing through the filter paper was recorded and a solidsconcentration was calculated as described above. Calculated solidsconcentration results are in Table 3.

Comparative Example D

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. An aqueous 0.1% SUPERFLOC 135solution (1.25 mL) was added to the slurry and the slurry was stirred. A35% aluminum hydroxide sulfate solution (0.035 mL, 7.16% Al₂O₃) wasadded to the slurry and the slurry was stirred. After 30 seconds, anaqueous 0.1% PERCOL 7651 solution (0.5 mL, a cationic polyacrylamidecommercially available from Ciba Specialty Chemical Corp., Tarrytown,N.Y.) was added to the slurry and the slurry was stirred. After 15seconds, the stirring was stopped, and the beaker contents werefiltered. The volume of the liquid passing through the filter paper wasrecorded and a solids concentration was calculated as described above.Calculated solids concentration results are in Table 3.

TABLE 3 Calculated Solids Concentration (% by weight) vs. Time (minutes)0.5 min 1 min 2 min 3 min 4 min 5 min Example 3 5.68 15.58 38.20 49.5549.55 55.01 Comp. Ex. D 3.15 4.01 7.16 20.17 31.67 42.41

Example 3 and Comparative Example D are examples offlocculant-coagulant-flocculation dewatering processes. As can be seenin Table 3, the calculated solids concentration of the product ofExample 3, which contained 100 ppm SiO₂ as polysilicate microgel, 5 ppmanionic polyacrylamide (APAM), 10 ppm Al₂O₃ as aluminum hydroxidesulfate, and 2 ppm cationic polyacrylamide (CPAM), was greater than thesolids concentration of the product of Comparative Example D, whichcontained 5 ppm APAM, 10 ppm Al₂O₃ as aluminum hydroxide sulfate, and 2ppm CPAM but did not contain polysilicate microgel.

Example 4

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. Aqueous polysilicate microgelsolution (2.5 mL, 1% SiO₂) was added to the slurry and the slurry wasstirred. An aqueous 5% aluminum chlorohydrate solution (1 mL, 5.85%Al₂O₃, commercially available from Gulbrandsen Chemicals, LaPorte, Tex.)was added to the slurry and the slurry was stirred. Sodium hydroxide(1.2 mL, 0.3 N) was then added to the slurry to raise the pH to 8.4. Anaqueous 0.1% SUPERFLOC 135 solution (3.75 mL) was added to the slurryand the slurry was stirred. After 15 seconds, the stirring was stopped,and the beaker contents were filtered. The volume of the liquid passingthrough the filter paper was recorded and a solids concentration wascalculated as described above. Calculated solids concentration resultsare in Table 4.

Comparative Example E

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to theslurry in the beaker to bring the clay solids concentration to 2% byweight in the slurry and the slurry was stirred. Aqueous 2.85% sodiumsilicate solution (0.877 mL) was added to the slurry and the slurry wasstirred. An aqueous 5% aluminum chlorohydrate solution (1 mL, 5.85%Al₂O₃) was added to the slurry and the slurry was stirred. Sodiumhydroxide (1.2 mL, 0.3 N) was then added to the slurry to raise the pHto 8.4. An aqueous 0.1% SUPERFLOC 135 solution (3.75 mL) was added tothe slurry and the slurry was stirred. After 15 seconds, the stirringwas stopped, and the beaker contents were filtered. The volume of theliquid passing through the filter paper was recorded and a solidsconcentration was calculated as described above. Calculated solidsconcentration results are in Table 4.

TABLE 4 Calculated Solids Concentration (% by weight) vs. Time (minutes)0.5 min 1 min 2 min 3 min 4 min 5 min Example 4 3.39 6.37 24.45 30.4030.40 30.40 Comp. Ex. E 2.50 2.78 3.25 3.71 4.25 4.87

As can be seen in Table 4, the calculated solids concentration of theproduct of Example 4, which contained 100 ppm SiO₂ as polysilicatemicrogel, 117 ppm Al₂O₃ as aluminum chlorohydrate solution, and 15 ppmanionic polyacrylamide (APAM), was greater than the solids concentrationof the product of Comparative Example E, which contained 100 ppm sodiumsilicate, 117 ppm Al₂O₃ as aluminum hydroxide sulfate and 15 ppm APAM.

Example 5

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. Aqueous polysilicate microgelsolution (2.5 mL, 1% SiO₂) was added to the slurry and the slurry wasstirred. Sodium hydroxide (0.3 mL, 0.5 N) was then added to the slurryto raise the pH to 8.4. An aqueous 0.1% SUPERFLOC 135 solution (1.25 mL)was added to the slurry and the slurry was stirred. An aqueous 1%Agefloc A50HV solution (1 mL, a low molecular weight polyamine coagulantcommercially available from Ciba Specialty Chemical Corp., Tarrytown,N.Y.) was added to the slurry and the slurry was stirred. After 30seconds, an aqueous 0.1% PERCOL 7650 solution (1.5 mL, a cationicpolyacrylamide commercially available from Ciba Specialty ChemicalCorp., Tarrytown, N.Y.) was added to the slurry and the slurry wasstirred. After 15 seconds, the stirring was stopped, and the beakercontents were filtered. The volume of the liquid passing through thefilter paper was recorded and a solids concentration was calculated asdescribed above. Calculated solids concentration results are in Table 5.

Comparative Example F

A clay fines slurry (2.5 g, 12.4% solids) retained from oil sandssolvent recovery unit was added to a beaker. Water was added to thebeaker to bring the clay solids concentration in the slurry to 2% byweight and the slurry was stirred. Sodium hydroxide (0.1 mL, 0.5 N) wasthen added to the slurry to raise the pH to 8.4. An aqueous 0.1%SUPERFLOC 135 solution (1.25 mL) was added to the slurry and the slurrywas stirred. An aqueous 1% Agefloc solution (1 mL) was added to theslurry and the slurry was stirred. After 30 seconds, an aqueous 0.1%PERCOL 7650 solution (1.5 mL, a cationic polyacrylamide commerciallyavailable from Ciba Specialty Chemical Corp., Tarrytown, N.Y.) was addedto the slurry and the slurry was stirred. After 15 seconds, the stirringwas stopped, and the beaker contents were filtered. The volume of theliquid passing through the filter paper was recorded and a solidsconcentration was calculated as described above. Calculated solidsconcentration results are in Table 5.

TABLE 5 Calculated Solids Concentration (% by weight) vs. Time (minutes)0.5 min 1 min 2 min 3 min 4 min 5 min Example 5 5.65 24.33 39.84 43.2943.29 43.29 Comp. Ex. F 3.88 6.26 15.22 28.01 38.91 42.19

Example 5 and Comparative Example F are examples offlocculant-coagulant-flocculation dewatering processes. As can be seenin Table 5, the calculated solids concentration of the product ofExample 5, which contained 100 ppm SiO₂ as polysilicate microgel, 5 ppmanionic polyacrylamide (APAM), 40 ppm low molecular weight coagulant,and 2 ppm cationic polyacrylamide (CPAM), was greater than the solidsconcentration of the product of Comparative Example F, which containedwhich 5 ppm anionic polyacrylamide (APAM), 40 ppm low molecular weightcoagulant, and 2 ppm cationic polyacrylamide (CPAM), but did not containpolysilicate microgel. Significantly, the rate of dewatering for theproduct of Example 5 was much faster than the rate of dewatering for theproduct in Comparative Example F.

1. A process for treating a tailings stream which comprises sand, clayfines and water, the process comprising (a) contacting a polysilicatemicrogel, an anionic polyacrylamide and a multivalent metal compound ora low molecular weight cationic organic polymer with the tailings streamto flocculate the sand and clay fines producing flocculated solids, and(b) separating the flocculated solids from the stream.
 2. A processaccording to claim 1 wherein the tailings stream is a coarse tailings, afine tailings or a froth treatment tailings produced in a process forextracting bitumen from an oil sands ore.
 3. A process according toclaim 1 wherein the multivalent metal compound and/or low molecularweight cationic organic polymer is added and then the anionicpolyacrylamide is added to the tailings stream.
 4. A process accordingto claim 1 wherein the addition sequence to the tailings stream is (1) afirst polymer, which is the anionic polyacrylamide, then (2) amultivalent metal compound and/or low molecular weight cationic organicpolymer, and then (3) a second polymer, which is a cationic or anionicpolyacrylamide, wherein the polysilicate is added prior to or afteradditions (1), (2) or (3).
 5. A process according to claim 4 wherein thefirst polymer is an anionic polyacrylamide and the second polymer is acationic polyacrylamide.
 6. A process according to claim 4 whereinpolysilicate microgel is added after addition (1).
 7. A processaccording to claim 4 wherein polysilicate microgel is added afteraddition (2).
 8. A process according to claim 4 wherein polysilicatemicrogel is added after addition (3).
 9. A process according to claim 1wherein a multivalent metal compound is added in step (a) and themultivalent metal is calcium, magnesium, aluminum, iron, titanium,zirconium or a combination of two or more thereof.
 10. A processaccording to claim 9 wherein the multivalent metal compound is calciumchloride, calcium sulfate, calcium hydroxide, aluminum sulfate,magnesium sulfate, and aluminum chloride, polyaluminum chloride,polyaluminum sulfate, or aluminum chlorohydrate.
 11. A process accordingto claim 10 wherein the multivalent metal compound is calcium sulfate,aluminum sulfate, polyaluminum sulfate, polyaluminum chloride, oraluminum chlorohydrate.
 12. A process according to claim 1 wherein a lowmolecular weight cationic organic polymer is added in step (a) and thelow molecular weight cationic organic polymer is selected from the groupconsisting of polyethylene imine, polyamines, polycyandiamideformaldehyde polymers, diallyl dimethyl ammonium chloride polymers,diallylaminoalkyl (meth)acrylate polymers, dialkylaminoalkyl(meth)acrylamide polymers, a copolymer of acrylamide and diallyldimethyl ammonium chloride, a copolymer of acrylamide anddiallylaminoalkyl (meth)acrylates, a copolymer of acrylamide anddialkyldiaminoalkyl (meth)acrylamide, and a copolymer of dimethylamineand epichlorohydrin.
 13. A process according to claim 1 whereinseparating is accomplished by using a thickener, hydrocyclone, or acentrifuge, or by decantation or filtration.